The use of implantable fluid medication dispensers is well known. These devices typically include a medication reservoir within a generally cylindrically shaped housing. Some form of fluid flow control is also provided to control or regulate the flow of fluid medication from the reservoir to the outlet of the device for delivery of the medication to the desired location, usually through a catheter. The flow control may be provided by a pumping or metering device such as disclosed in U.S. Pat. No. 4,692,147 issued to Duggan. Other forms of flow control are disclosed in U.S. Pat. Nos. 3,951,147 and 4,360,019.
All implantable fluid medication dispensers must also include some means to replenish the fluid medication in the medication reservoir. The previously mentioned U.S. Pat. Nos. 4,692,147 to Duggan and 3,951,147 to Tucker et al. disclose typical reservoir refill assemblies. Both include an opening or port through which a resealable septum may be accessed. To refill the reservoir a hypodermic needle is inserted through the septum and into a chamber between the septum and a needle stop, which may be a plug or filter. The medication is injected under pressure into the chamber and flows into the Reservoir.
One disadvantage which exists with respect to currently used fluid medication dispensers is the weight of the devices. Weight is a critical factor with respect to both the physical and psychological comfort of the patient. In devices where the fluid medication reservoir is pleated such as in the typically used bellows configuration, in order to insure that the medication reservoir has minimal dead space when the convulsions of the pleats of the bellows are compressed, current devices utilize a bulkhead with a boss configured to mate with the interior of the bellows when compressed. This raised boss adds considerably to the overall weight of the fluid medication dispenser. Therefore, it would be desirable to provide a medication delivery device having a reduced weight.